1. Field of the Invention
This invention relates to the field of information networks, and more particularly relates to a router capable of routing information over a network.
2. Description of the Related Art
Today's networks carry vast amounts of information. High bandwidth applications supported by these networks include streaming video, streaming audio, and large aggregations of voice traffic. In the future, these demands are certain to increase. To meet such demands, an increasingly popular alternative is the use of lightwave communications carried over fiber optic cables. The use of lightwave communications provides several benefits, including high bandwidth, ease of installation, and capacity for future growth.
The synchronous optical network (SONET) protocol is among those protocols designed to employ an optical infrastructure and is widely employed in voice and data communications networks. SONET is a physical transmission vehicle capable of transmission speeds in the multi-gigabit range, and is defined by a set of electrical as well as optical standards. SONET networks have traditionally been protected from failures by using topologies that support fast restoration in the event of network failures. Their fast restoration time makes most failures transparent to the end-user, which is important in applications such as telephony and other voice communications. Existing schemes rely on techniques such as 1-plus-1 and 1-for-1 topologies that carry active traffic over two separate fibers (line switched) or signals (path switched), and use a protocol (Automatic Protection Switching or APS), or hardware (diverse protection) to detect, propagate, and restore failures.
In routing the large amounts of information between the nodes of an optical network, it is desirable to have a fast, efficient method for finding the most preferable path through that network. For example, in the case of voice communications, the failure of a link or node can disrupt a large number of voice circuits. The detection of such faults and the restoration of information flow must often occur very quickly to avoid noticeable interruption of such services. For most telephony implementations, for example, failures must be detected within about 10 ms and restoration must occur within about 50 ms. The short restoration time is critical in supporting applications, such as current telephone networks, that are sensitive to quality of service (QoS) because such detection and restoration times prevent old digital terminals and switches from generating alarms (e.g., initiating Carrier Group Alarms (CGAs)). Such alarms are undesirable because they usually result in dropped calls, causing users down time and aggravation. Restoration times exceeding 10 seconds can lead to timeouts at higher protocol layers, while those that exceed 1 minute can lead to disastrous results for the entire network.
In a SONET network, a failure of a given link results in a loss of signal (LOS) condition at the nodes connected by that link (per Belicore's recommendations in GR-253 (GR-253: Synchronous Optical Network (SONET) Transport Systems, Common Generic Criteria, Issue 2 [Bellcore, December 1995], included herein by reference, in its entirety and for all purposes)). The LOS condition propagated an Alarm Indication Signal (AIS) downstream, and Remote Defect Indication (RDI) upstream (if the path still exists), and an LOS defect locally. The defect is upgraded to a failure 2.5 seconds later, which causes an alarm to be sent to the Operations System (OS) (per GR-253). When using SONET, the handling of the LOS condition should follow Bellcore's recommendations in GR-253 (e.g., 3 ms following a failure, an LOS defect is detected and restoration should be initiated). This allows nodes to inter-operate, and co-exist, with other network equipment WE) in the same network. The arrival of the AIS at a node causes the node to send a similar alarm to its neighbor and for that node to send an AIS to its own neighbor, and so on. Under GR-253, each node is allowed only a certain amount of time in which to forward the AIS, and so quickly propagate the indication of a failure.
As can be seen, a network element in such environments must be able to quickly detect and address failures such as those discussed above. To enable the detection, and so correction, of such failures, it is desirable to provide the ability to monitor the operation of the network element, without detrimentally affecting the network element's operation. Also desirable is the ability to predict the occurrence of failures, so that corrective action may be taken in advance of any failures that might occur.